A frequent question in the management of primary brain tumors in the post-treatment period is whethei a new or expanding brain lesion observed on CT or MR imaging represents recurrent tumor or treatment effects. This is of particular concern in the management of patients with previously treated low grade or anaplastic gliomas. PET imaging can provide "functional" information, in addition to that obtained by MRI, which may be useful in patient management decisions. Amino acid imaging of tumors with positron emission tomography (PET) dates back two decades, and the consensus opinion that is amino acid images provide better information with respect to brain tumor localization than fluorodeoxyglucose (FDG). We propose an initial small series of PET imaging studies that compare a fluorine-18 labeled amino acid analogue, 3-fluoroaminocyclobutane carboxylic acid (3-[18F]-FACBC) to carbon-11 labeled [methyl-11c]-l-methionine, the amino acid currently used in most brain tumor imaging studies and considered to be the "gold standard". Compared to [methyl-11c]-L-methionine, [18F]-FACBC provides substantial logistical and cost-effective benefits for brain tumor imaging in a busy nuclear medicine department; this is due to the longer half-life of [18F] (t 1/2=110 min) compared to [11C] (t1/2=20 min). The goals of this proposal are: 1) to obtain sufficient [18F]-FACBC biodistribution and dosimetry data in human subjects that will support the submission of an investigational new drug (IND) application to the Food and Drug Agency (FDA); 2) to show that [18F]-FACBC has equal or better brain tumor imaging characteristics than [methyl-11C]-L-methionine, and has the potential to improve the "early" detection of recurrent or progressive primary brain tumors.